How to get OpenCL functioning for GPU rendering, AMD GPU?
From Blender manual on OpenCL support:


  OpenCL is supported for GPU rendering with AMD graphics cards. (We only support graphics cards with GCN architecture 2.0 and above).


2.79 release log says:


  Due to various issues with drivers for AMD GCN 1.0 architecture, those cards are no longer supported for Cycles rendering "


The support was dropped so you need Blender 2.78c version or a newer card.